This invention relates in general to slip joints for transmitting rotational force from a source to a driven mechanism, while accommodating a limited amount of relative axial movement therebetween. In particular, this invention relates to an improved structure for a rolling ball spline type of slip joint that is formed from two tubular members and to a method of manufacturing same.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a first universal joint is usually connected between the output shaft of the engine/transmission assembly and a first end of the driveshaft assembly, while a second universal joint is usually connected between a second end of the driveshaft assembly and the input shaft of the axle assembly. The universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft assembly to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes thereof.
Not only must a typical drive train system accommodate a limited amount of angular misalignment between the source of rotational power and the rotatably driven device, but it must also typically accommodate a limited amount of relative axial movement therebetween. For example, in most vehicles, a small amount of such relative axial movement frequently occurs when the vehicle is operated. To address this, it is known to provide a slip joint in the driveshaft assembly. A typical slip joint includes first and second members that have respective structures formed thereon that cooperate with one another for concurrent rotational movement, while permitting a limited amount of axial movement to occur therebetween. Two types of slip joints are commonly used in conventional driveshaft assemblies, namely, a sliding spline type and a rolling ball spline type.
A typical sliding spline type of slip joint includes male and female members having respective pluralities of splines formed thereon. The male member is generally cylindrical in shape and has a plurality of outwardly extending splines formed on the outer surface thereof. The male member may be formed integrally with or secured to an end of the driveshaft assembly described above. The female member, on the other hand, is generally hollow and cylindrical in shape and has a plurality of inwardly extending splines formed on the inner surface thereof. The female member may be formed integrally with or secured to a yoke that forms a portion of one of the universal joints described above. To assemble the slip joint, the male member is inserted within the female member such that the outwardly extending splines of the male member cooperate with the inwardly extending splines of the female member. As a result, the male and female members are connected together for concurrent rotational movement. However, the outwardly extending splines of the male member can slide relative to the inwardly extending splines of the female member to allow a limited amount of relative axial movement to occur between the engine/transmission assembly and the axle assembly of the drive train system.
A typical rolling ball spline type of slip joint includes male and female members having respective pluralities of longitudinally extending grooves formed thereon. The male member is generally cylindrical in shape and has a plurality of inwardly extending grooves formed in the outer surface thereof. The male member may be formed integrally with or secured to an end of the driveshaft assembly described above. The female member, on the other hand, is generally hollow and cylindrical in shape and has a plurality of outwardly extending grooves formed in the inner surface thereof. The female member may be formed integrally with or secured to a yoke that forms a portion of one of the universal joints described above. To assemble the slip joint, the male member is inserted within the female member such that the inwardly extending grooves of the male member are aligned with the outwardly extending grooves of the female member. A plurality of balls is disposed in each of the aligned pairs of the grooves. As a result, the male and female members are connected together for concurrent rotational movement. However, the male member can slide relative to the inwardly extending splines of the female member to allow a limited amount of relative axial movement to occur between the engine/transmission assembly and the axle assembly of the drive train system.
The rolling ball spline type of slip joint is generally considered to be more desirable than the sliding spline type of slip joint because the amount of force that is required to effect relative axial movement between the male and female members is much smaller, particularly when relative axial movement is attempted while torque is being transmitted through the slip joint. However, the rolling ball spline type of slip joint is more complex in structure and more expensive to manufacture than the sliding spline type of slip joint. Also, in a rolling ball spline type of slip joint, either or both of the male and female members are usually initially formed by forging a solid member to a desired shape. Then, material is removed from either or both of the male and female members to form the longitudinally extending grooves therein. Although this manufacturing process has functioned satisfactorily, it has been found to be somewhat complicated and costly. Thus, it would be desirable to provide an improved structure for a rolling ball spline type of slip joint, and a method of manufacturing same, that is simpler in structure and less expensive to manufacture than previously known.